This Demonstration simulates the response of photosynthesis () to photosynthetic photon flux density PPFD (). The equations are based on the leaf model of photosynthesis  that predicts based on the most limiting of three processes: (1) the kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (or rubisco) for fixing , (2) the rate of RuBP regeneration associated with electron transport rates on the thylakoid membrane (RuBP), and (3) the rate in which inorganic phosphate, required for regenerating ATP from ADP, is released during the utilization of triose phosphate (TPU). While the functions associated with all three of these limiting processes are shown (Rubisco, RuBP, and TPU), the actual modeled rate of photosynthesis will be the lowest of the three processes. The modeled rates of photosynthesis are indicated by the net photosynthesis curve (solid black line). Vary any of the parameters and/or environmental conditions to see the impact on the modeled photosynthesis over the range of PPFD. The equations from the original model  have been corrected with the temperature functions from  for rubisco-limited photosynthesis, [2, 4, 6] for RuBP-limited photosynthesis, and  for TPU-limited photosynthesis. Changes in the environmental conditions introduce changes in the leaf intercellular concentration , which are not simulated here.
The leaf's environmental conditions include leaf intercellular concentration (), oxygen concentration (), and leaf temperature (°C).
The photosynthetic parameters include the maximum rate of carboxylation (), maximum rate of electron transport through photosystem II (), rate of triose phosphate utilization (), and rate of mitochondrial respiration ().
The temperature dependence of is derived using the data from  but with the temperature response of  modified as in  to normalize values to 25°C. Under the heading "RuBP-Limited Adjustments", you can vary the temperature optimum and the temperature at which falls to of its value at (). The default parameterization for these values are from  for tobacco grown at 25 °C, but values for a range of species are provided elsewhere . Changes in and only affect when . You can also vary the leaf absorbance (unitless), the ratio of photosystem II to photosystem I (unitless), the curvature of the PPFD response curve (unitless), and the quantum efficiency of PSII ΦPSII (unitless).
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